Device for converting fluid pressure into electrical quantity having linearity

ABSTRACT

A pressure-voltage transducer comprising: a pressure detector having an output shaft for converting a variation of fluid pressure into a mechanical displacement of said output shaft; a movable core extendibly connected to said output shaft of said pressure detector; an exciting winding for AC excitation; first and second induction windings inductively coupled to said exciting winding through said movable core, one end of said first and second induction windings providing first and second terminals, respectively, the other ends of said first and second induction windings being connected to each other; a first diode connected between said first terminal and said first induction winding; a second diode connected between said second terminal and said second induction winding; a first resistor connected between the ends of said first induction winding through said first diode; a second resistor connected between the ends of said second induction winding through said second diode; a first capacitor connected between the ends of said first induction winding and in parallel with said first resistor; and a second capacitor connected between the ends of said second induction winding and in parallel with said second resistor, whereby a DC voltage proportional to the mechanical displacement of said pressure output shaft is produced across said first and second terminals.

United States Patent [191 Kamazuka 1 DEVICE FOR CONVERTING FLUID PRESSURE INTO ELECTRICAL QUANTITY HAVING LINEARITY [75] Inventor: Isezi Kamazuka, Kariya, Japan [73] Assignee: Nippondenso Co., Ltd., Kariya-shi,

Japan [22] Filed: Nov. 29, 1971 21 Appl. No.: 202,756

Related US. Application Data [63] Continuation-in-part of Ser. No. 002,464, Jan. 13,

1970, abandoned.

[30] Foreign Application Priority Data Primary Examiner-Donald O. Woodiel A Attorney, Agent, or FirmCushman, Darby &

Cushman Apr. 23, 1974 [57 ABSTRACT A pressure-voltage transducer comprising: a pressure detector having an output shaft for converting a variation of fluid pressure into a mechanical displacement of said output shaft; a movable core extendibly connected to said output shaft of said pressure detector; an exciting winding for AC excitation; first and second induction windings inductively coupled to said exciting winding through said movable core, one end of said first and second induction windings providing first and second terminals, respectively, the other ends of said first and second induction windings being connected to each other; a first diode connected between said first terminal and said first induction winding; a second diode connected between said second terminal and said second induction winding; a first resistor connected between the ends of said first induction winding through said first diode; a second resistor connected between the ends of said second induction winding through said second diode; a first capacitor connected between the ends of said first induction winding and in parallel with said first resistor; and a second capacitor connected between the ends of said second induction winding and in parallel with said second resistor, whereby a DC voltage proportional to the mechanical displacement of said pressure output shaft is produced across said first and second terminals.

3 Claims, 2 D'PYFEEFFFFES? PATENTEBAPRZB I974 38056 1 7 ATTORNEY CROSS-REFERENCES TO RELATED APPLICATION This application is a continuation-in-part of a copending U. S. Pat. Application Ser. No. 2,464 filed on Jan. 13, 1970, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for converting the pressure of a fluid, such as air, water or oil into a linear electrical signal.

2. Description of the Prior Art Recently, it has been an increasingly common practice with automotive vehicles to detect the pressure in the engine intake manifold to thereby provide actuating signals for automatic control systems.

In the past, there has been known a device of this type for converting the pressure in the intake manifold of an engine into an electrical signal which device comprises, in combination, a diaphragm mechanism and a potentiometer.

The conventional device described above, however, is disadvantageous in that due to the sliding mechanical parts employed in the potentiometer itself, not only the life of the device itself tends to be short, but also the generation of mechanical noise is involved and the device also tends to become bulky. Moreover, due to the fact that the convertion of a pressure into an equivalent electrical quantity is performed entirely mechanically, there are other drawbacks of poor response characteristics and decreased accuracy.

SUMMARY OF THE INVENTION To overcome these deficiencies, the present invention has for its object the provision ofa device for converting a fluid pressure into a relatively large electrical quantity, said device comprising a differential transformer including an exciting winding for AC excitation and two induction windings inductively coupled to said exciting winding by way of a movable core such that the voltages induced in said induction windings are rectified and smoothed to produce a DC differential voltage, and a pressure detector for converting a fluid pressure into a mechanical displacement with the output shaft of said pressure detector being extendibly con nected to the movable core of said differential transformer, thereby decreasing the number of sliding mechanical parts as far as possible and thus extending the life of the device and improving the response characteristics and accuracy of the device.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates an electrical wiring diagram showing an embodiment of the differential transformer and a longitudinal sectional view showing an embodiment of the pressure detector, which are employed with the device of the present invention.

FIG. 2 is a characteristic diagram showing the output characteristic of the device according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, numeral 1 designates a pressure detector, 2 a casing, 3 a pressure inlet port opening into the casing 2 and communicating with the intake manifold of an engine for admitting the engine intake vacuum into the casing 2. Numerals 4 and 5 designate bellows having a vacuum therein and secured at one end face thereof so that the two bellows are disposed in the casing 2 as a unit-Numeral 6 designates a fixed shaft; 7 an output shaft, the bellows 4 and 5 being'bridged and supported at near the center in the casing 2 by the shafts 6 and 7. One end of the fixed shaft 6 is formed with a thread and is securely threaded to the bottom of the casing 2 and the other end is securely threaded to one end face of the bellows 4. On the other hand, one end of the output shaft 7 is provided with a threaded hollow portion in the axial direction and is extended through the top portion of the casing 2 and the other end of the output shaft 7 is secured to one end face of the bellows '5 in tension. Numeral 8 designates a shaft sealing member securely mounted around an opening formed at the top portion of the easing 2 through which the output shaft 7 extends, the sealing member hermetically sealing the opening and the output shaft 7. Numeral 9 designates a return spring mounted on the output shaft 7 and squeezed between one end face of the bellows 5 and the inner face of the top portion of the casing 2. Numeral l0 designates an AC power source; 11 a differential transformer; 12 a movable core; 13 a driving shaft secured to one end of the movable core 12 and securely threaded into the threaded hollow portion of the output shaft 7 by means of its threaded end. Numeral l4 designates an exciting winding for providing AC excitation from the AC power source 10; 15 and 16, first and second induction windings inductively closely coupled to the exciting winding 14 through the movable core 12. One end terminal of the first and second induction windings l5 and 16 are respectively connected to output terminals 19 and 20 through rectifying diodes 17 and 18, respectively. Numerals 21 and 22 designate smoothing resistors; 23 and 24, smoothing capacitors. The resistor 21 and the capacitor 23 are connected in parallel between the end terminals of the first induction winding 15 through the diode 17, while the resistor 22 and the capacitor 24 are connected in parallel between the end terminals of the second induction winding 16 through the diode l8.

With the construction described above, the operation of the device according to the present invention will be described hereinafter. When the engine intake manifold vacuum which is to be admitted into the casing 2 of the pressure detector 1 is zero, as shown in FIG. 1, the bellows 4 and 5 each having a vacuum therein are contracted and the movable core 12 is placed between the first and second induction windings l5 and 16. Thus, the windings l5 and 16 are inductively coupled to the exciting winding 14 through the movable core 12 in an equal degree so that their voltage inducing actions are cancelled inducing no voltage and thus producing no DC voltage across the output terminals 19 and 20. Then, when a vacuum in the engine intake manifold is admitted into the casing 2, the bellows 4 and 5 expand in response to the vacuum against the spring force of the spring 9 and thus the movable core 12 is correspondingly moved up in the direction of an arrow A. When this occurs, the first induction winding 15 increases its degree of inductive coupling with the exciting winding 14 so that the induced voltage in the first inductive winding 15 becomes larger than that in the second induction winding 16. This produces across the output terminals 19 and 20 the DC difference voltage between the voltages induced in the windings l5 and 16 and is then rectified and smoothed.

. FIG. 2 illustrates the output characteristic of the device of the present invention in which the straight line B represents the output voltage V of the differential transformer 11 corresponding to the displacement L of the movable core 12 and the crossing point C of the straight line B and the horizontal axis represents the point where the movable core 12 lies between the first and second induction windings 15 and 16 as shown in FIG. 1 and at this time the output voltage of the differential transformer 11 is zero. Then, as the movable core 12 moves away in the direction of the arrow A from the position of FIG. 1 the output voltage of the differential transformer 11 becomes positive, whereas as the movable core 12 moves away from the position of FIG-'1 in the direction opposite to the direction of the arrow A the output voltage of the differential transformer 11 becomes negative. As for the setting of the point C, since the driving shaft 13 carrying the movable core 12 is threadedly fitted into the treaded hollow portion of the output shaft 7, the setting of the point C can be effected as desired by adjusting the length of fitting between the hollow portion and the shaft 13.

On the other hand, by increasing the degree of coupling among the exciting winding 14 and the first and second induction windings I5 and 16 inductively coupled to the exciting winding 14 through the movable core 12 and by selecting the AC power source to be such that produces a large output, a relatively large output can be obtained from the differential transformer 11 and this output, as such, can provide the required actuating signals for automatic control systems without amplifying it.

Whilethe present invention has been described by,

means of the above-mentioned embodiment in which negativetpressure is employed, positive pressure as well as a pressure continuously varying from negative to positive values can also be converted into a DC voltage having linearity in the similar manner. It also goes without saying that any'fluids including air, water and oil can be suitably used as a medium for providing the required negative and positive pressures. Moreover, while in the embodiment described above the pressure detector 1 has been shown as employing the bellows 4 and 5, other forms of the detector employing diaphragms, pistons or the like may also be'used effectively. Furthermore, means for extendibly connecting the driving shaft 13 carrying the movable core 12 with the output shaft 7 of the pressure detector 1 is not limited as a matter of course to those which provide the connection by means of threads, but any other means such as pins which are capable of providing a semipermanent coupling may also be employed effectively. Still furthermore, while in the embodiment described above the pressure detector 1 and the differential transformer 11 have been shown as separate units, the pressure detector 1 may have the differential transformer 11 incorporated as a part thereof.

It is now evident from the foregoing description that according to the present invention there is a remarkable effect in that since the device of the present invention comprises a differential transformer including an exciting winding for AC excitation and 'two induction windings inductively coupled to the exciting winding through a movable core such that the voltages induced in the two induction windings are rectified and smoothed to produce the DC difference voltage and a pressure detector for converting a fluid pressure into a mechanical displacement with the output shaft of the pressure detector being extendibly connected to the movable core of the differential transformer, a linear electrical signal and corresponding to a fluid pressure can be obtained from the differential transformer and moreover this electrical quantity is obtained in the form of an output corresponding to the difference between the induced voltages in the two induction windings of the differential transformer so that it is possible to ensure an excellent temperature characteristic and voltage characteristic, to minimize the effect of disturbance, and convert fluid pressure into electrical quantity with improved accuracy. There is a further remarkable effect in that by selecting an AC power source which provides large output to supply the exciting winding and by increasing the degree of inductive coupling among the exciting winding and the two induction windings inductively coupled to the exciting winding through the movable core, a relatively large output can be obtained from the differential transformer and thus it is possible to actuate automatic control systems with this output without amplifying it. There is a still further remarkable effect in that the frequency of the AC exciting power source can be increased to a relatively high level without any trouble and thus it is possible to employ half-wave rectification instead of full-wave rectification, simplify the smoothing operation, reduce the number of component parts and hence the manufacturing cost, and make the device smaller and lighter. There is a still further remarkable effect in that by reducing the number of sliding mechanical parts to a minimum, improved response characteristic and elimination of mechanical noise are ensured and at the same time damage due to wear and the like are prevented thus ensuring a considerably extended service life. There is a still further remarkable effect in that since the output shaft of the pressure detector is extendibly connected to the movable core of the differential transformer,-the setting of the zero output point for the differential transformer can be effected as desired and with a considerable ease by adjusting the position of the movable core relative to the two induction windings.

I claim:

1. An engine intake manifold pressure transducer an exciting winding for AC excitation;

first and second induction windings inductively coupled to said exciting winding through said movable core, one end of said first and second induction windings providing first and second terminals respectively, the other ends of said first and second induction windings being connected with each other;

means for half wave rectifying the current flowing through said first and second induction windings including a first diode connected between said first terminal and said first induction winding and a second diode connected between said second terminal and said second induction winding;

a first resistor connected between the ends of said first induction winding through said first diode;

a second resistor connected between the ends of said second induction winding through said second di- 1, wherein said movable core is threadedly secured to said output shaft of said pressure detector.

3. A pressure-voltage transducer according to claim 1, wherein said pressure detector further includes a spring set between said casing and the other end of said bellows under the application of an initial load. 

1. An engine intake manifold pressure transducer comprising: a pressure detector for detecting engine intake manifold pressure including a casing having an inlet port communicating with fluid, at least one sealed, substantially evacuated bellows mounted in said casing with one end secured to said casing, an output shaft connected to the other end of said bellows for converting a variation in manifold pressure into a mechanical displacement of said output shaft and a shaft sealing member for holding and guiding said output shaft; a movable core extendibly connected to said output shaft of said pressure detector; an exciting winding for AC excitation; first and second induction windings inductively coupled to said exciting winding through said movable core, one end of said first and second induction windings providing first and second terminals respectively, the other ends of said first and second induction windings being connected with each other; means for half wave rectifying the current flowing through said first and second induction windings including a first diode connected between said first terminal and said first induction winding and a second diode connected between said second terminal and said second induction winding; a first resistor connected between the ends of said first induction winding through said first diode; a second resistor connected between the ends of said second induction winding through said second diode; a first capacitor connected in pArallel with said first resistor and between the ends of said first induction winding; and a second capacitor connected in parallel with said second resistor and between the ends of said second induction winding, whereby a half rectified DC voltage proportional to the displacement of said pressure output shaft is produced across said first and second terminals.
 2. A pressure-voltage transducer according to claim 1, wherein said movable core is threadedly secured to said output shaft of said pressure detector.
 3. A pressure-voltage transducer according to claim 1, wherein said pressure detector further includes a spring set between said casing and the other end of said bellows under the application of an initial load. 